The application of natural materials has been widely researched in the medical and cosmetic fields for their biocompatibility such as their histocompatibilities and biodegradability. In particular, various uses can be conceived by solidification or formation of insoluble hydrogels by means of chelating with salts or crosslinking reactions.
For example, in recent years, research relating to the function of carbohydrate chains has become more active, making it clear that they play a considerable role in cell adhesion and viral infection. The carbohydrates in mammals exist mostly as composites such as glycoproteins and glycolipids, with some of these carbohydrate chains contributing to specific functional expressions. For this reason, these types of substances containing carbohydrate chain are often biologically active, but in practice, present problems in terms of their handling and cost.
On the other hand, in plants and marine organisms, carbohydrate chains exist as macromolecular substances for the skeletal structures of the organisms. Cellulose, pectin, gum arabic, polygalactomannan, arginic acid and the like are contained in plants and algae, and are macromolecular substances with high viscosity capable of being cheaply mass-collected. Additionally, chitin/chitosans are widely distributed in the exoskeletons of insects and the shells of crustaceans such as crabs and lobsters, glucosamin which is the constituent carbohydrate thereof having the function of an elicitor for protecting against infection and decomposition.
Since these carbohydrates exist as polysaccharides having extremely high molecular weights and also have high viscosity, their application to medicine such as in wound dressings, artificial skin, implants used in oral surgery or plastic surgery, hemostatics and adhesives, or to cosmetics such as humectants has been considered, but their range of application is limited due to the difficulty of chemically modifying them with regard to solubility in solvents and the like in comparison to proteinous ingredients.
Chitin/chitosans, which are unique even among polysaccharides, contain amino groups as constituent carbohydrate units, so that their use in conjunction with chemical crosslinking agents such as isocyanates, aldehydes and carbodiimides in wound dressings, anti-adhesion materials and decomposing absorbents has been studied.
However, chitins are not soluble in water due to their crystallinity, which is based on hydrogen bonds, and must be decomposed to low-molecular weight substances by means of hydrolysis or partially deacetylated in order to prepare them to be suitable for application to a wide range of industrial fields including medicine. Additionally, chitosans with increased carbohydrate units with amino groups exposed by active deacetylation for the purposes of improving the physical properties of chitins are soluble in acidic solvents including dilute organic acids, but are still extremely thick, making them difficult to handle in wound dressings and biological adhesion which are required to be easily worked on the scene of medical treatment. Additionally, since the thick chitosan solution does not retain a physiological pH, it is difficult to freely add physiologically active reagents used for therapeutic purposes, and there is the problem of toxicity when used with free chemical crosslinking agents, thus limiting the possibilities of use in the field of health care including medicine.